Referring to FIGS. 1 and 2, turbine vanes in a gas turbine engine are exposed to high temperature combustion gas which imparts an intensive heat load onto the vanes. Since aerodynamic design of turbine vanes stipulates a thin trailing edge, the heat load leads to a chordwise temperature gradient in the vane. The thinner wall at the trailing edge means a lower thermal mass and thus translates into experiencing a higher temperature than the thicker leading edge under steady state conditions. During transient conditions such as engine start-up (See FIG. 1) or shutdown (See FIG. 2), the thin trailing edge would heat-up or cool-down faster than the thicker leading edge. The resulting temperature difference between the leading edge and the trailing edge could be much more severe under these transient conditions than the temperature difference experienced under steady state conditions.
The temperature gradient causes the leading edge to expand differently from the trailing edge and consequently generates thermal stress at the blade root where it joins vane inner and outer platforms (not shown). The two platforms actually make the stressing condition worse by forcing the leading edge deformation onto the trailing edge. Because of the relatively thin wall thickness at the trailing edge, the thermal stress is greater at the trailing edge than at the leading edge. Also, since the shutdown conditions produce high tensile stress, the thermal stress is more damaging at shutdown than at start-up conditions.
Due to the severity of these thermal stresses, it is necessary to maintain the thermal stresses at an acceptable level for component durability. That is, however, not always possible for a given engine operating condition and, in particular, when the turbine engine component is composed of low strength materials. Therefore, there exists a need to lower thermal stress at the vane trailing edge, especially during transient conditions such as engine shutdown, across a broad range of engine operating conditions for turbine vanes of any composition in order to ensure robust component life.